Chess is chess. OTB or online is still the same game, so they are more or less the same. The few differences (which are more severe for some and especially so at the highest levels of play) may include:
- "Tunnel Vision" of a sorts where someone spots chess ideas more effectively with 3D pieces versus a 2D computer screen or vice-versa. It messes with the depth perception of some who spend most of their chess in OTB or online, but not the other.
- physical atmosphere of playing in an OTB Tournament Hall versus in front of a computer monitor at home; the atmosphere is very different and that impacts some players used to one, but not the other
- Perhaps the biggest factor: Time Control. Online is usually much shorter than OTB.
Congratulations on your recent chess win 
However, 1250 chess.com is not immensely high for OTB events; I am guessing your Boston Chess Club friend is not as "regular" as they lead on? One other consideration might be that just because one plays OTB, that doesn't magically make them stronger. In this case, a lot of weaker players might join an OTB chess club (not saying it is the case for your friend but it might be the case).
In short, I don't think the transition from online to OTB (or vice-versa) is that big of a deal for most, but there are differences that can impact it more for some people; likewise, playing online or OTB is a different environment, so one can't assume an OTB player is better than an online player by that fact alone.
I started playing chess 2 years ago on chess.com, I was once rated 560 and now got over 1250. At work I met someone who plays at the Boston chess clubs in tourneys. He challenged me to an otb game, which I have little experience, but I took the challenge and won pretty easily. I was shocked that I won the way I did, cause I figured playing otb was different then online. Would playing thousand of games online really help me compete in the fide tournaments or is this just a fluke and I should start playing more games otb to eventually compete in these events?